This invention relates to a light scanning optical system for an image output scanner using an electro-mechanical light modulator.
An image output scanner is an apparatus which is used in facsimile or the like to scan the image of an original such as a document or the like and put out the image as image information by a light or electrical signal. Various forms of such image output scanner are known.
For example, many of the image output scanners used in popular PPC copying machines are of the type in which an original is scanned by the light of a halogen lamp or the like and the reflected light therefrom is directly imaged on an electrophotographic photosensitive member. Besides these, there is a method whereby, as in a laser beam printer, the image of an original is converted into an electrical signal, whereafter on the basis of this signal, a light modulator is used to modulate a laser beam, which in turn is imaged on a photosensitive member.
Also, in recent years, the development of the integrated circuit technique has proposed an image output scanner using an electro-mechanical light modulator having a number of deflecting elements on a base.
The general construction of the above-mentioned image output scanner will hereinafter be described with reference to the accompanying drawings.
FIG. 1 schematically shows an example of the image output scanner using the above-described electro-mechanical light modulator (hereinafter simply referred to as the light modulator). In FIG. 1, reference numeral 1 designates a light source such as a tungsten lamp, reference numeral 2 denotes an irradiating optical system, reference numeral 3 designates the light modulator, reference numeral 4 denotes a projection optical system, reference numeral 5 designates a reflecting mirror, and reference numeral 6 denotes a photosensitive drum.
The light from the lamp 1 is applied onto the light modulator 3 by the irradiating optical system 2, and only the necessary image signal reflected light is condensed on the photosensitive drum 6 by the projection optical system 4 via the reflecting mirror 5. In such an image output scanner, various configurations of the light modulator 3 are now conceived.
FIG. 2A is an enlarged schematic perspective view of an example of such light modulator 3, and FIG. 2B is an enlarged schematic side view thereof.
In FIG. 2, reference character 3a designate mirror picture element plates adapted to be bent upwardly or downwardly by electro-mechanical means. As shown in FIG. 2B, the direction of the reflected light 7 from the downwardly bent mirror picture element plate 3a (indicated by dotted line) differs from the direction of the reflected light (indicated by solid line) from the unbent mirror picture element plate 3a. By thus changing the direction of each of the mirror picture element plates 3a in conformity with an image signal input to the light modulator 3, it is possible to form an electrostatic latent image corresponding to the image signal on the surface of the photosensitive drum. The electrostatic latent image is converted into a visible image by the well-known electrophotographic process.
However, in the image output scanner as described above, the direction of bending of the mirror picture element plate 3a is downwardly inclined without torsion relative to the side of the mirror picture element plate 3a as shown in FIG. 2B and therefore, separation of the signal light and the unnecessary reflected light 7 becomes difficult when the diffraction in the image space is considered. As a result, the distance between the light modulator 3 and the projection optical system 4 must be made long until the two diffracted lights can be separated from each other. This is nothing but making the optical system large in the lateral direction. Also, making the distance between the light modulator 3 and the projection optical system 4 long leads to a result that the intensity of light on the photosensitive drum 6 is reduced when it is assumed that the intensity of light of the light source is constant, and to prevent it, it becomes necessary that the angle of view at which the light source subtends the lens of the irradiating optical system 2 be made great. This means that the optical system is made large in the direction of height, which in turn poses a serious problem in making the image output scanner compact.
It is an object of the present invention to provide a light scanning optical system which can efficiently separate unnecessary diffracted light and image signal light from each other.
It is a further object of the present invention to provide a compact light scanning optical system which can efficiently perform the above separation as well.
It is still a further object of the present invention to provide a light scanning optical system which is excellent in quality of printing and compact.
According to the present invention, in order to solve the above-noted problems, there is provided a light scanning optical system of an image output scanner in which a light beam incident from a light source through an irradiating optical system is applied to an electro-mechanical light modulator comprising a number of elements capable of deflecting said incident light beam in at least two directions in conformity with an input signal and arranged in the main scan direction (the direction perpendicular to the plane of the drawing sheet of FIG. 1), and image information is prepared by the change-over of the direction of deflection of each of said elements, whereafter only a signal light is projected onto a photosensitive member by a projection optical system, characterized in that the shape of at least one of said irradiating optical system and said projection optical system is flat in the main scan direction.